1. Field of the Invention
This invention relates to soundproofing materials and more particularly, to the use of tetrapod-shaped whisker particles of zinc oxide as a soundproofing or vibration-damping or deadening material utilizable in the fields of sound insulation, sound absorption, vibration damping and vibration insulation.
2. Description of the Prior Art
Various types of soundproofing and vibration-damping materials have been heretofore employed in various industries of automobiles, railroad vehicles, buildings and building materials, domestic appliances such as speakers, record players, video tape recorders, television sets, washing machines, vacuum cleaners, refrigerators, air conditioners, tableware cleaners and the like, industrial instruments, elevators, ducts, office appliances such as printers, plotters, key boards, duplicators and the like, kitchen utencils, stage reflectors, and the like.
Broadly, noises can be classified into two categories including sounds or noises transmitted through air and noises transmitted though solid matter. The sound insulation and sound absorption are a kind of measure against the air transmitted sounds. The vibration damping and insulation are against the solid transmitted sounds. From an angle of noise control, the absorption of sound or vibration energy leads to sound absorption or vibration damping. The reflection of the energy results in sound or vibration insulation.
The term "soundproofing" relating to both sound and vibration may be classified into sound insulation, sound absorption, vibration damping and vibration insulation which depend on the type of energy and how the energy is dealt with.
The sound insulation is to intercept sound waves on the way of their transmission so that a transmitted sound level is made smaller than an initial sound level. Materials capable of reducing the sound energy are usable as a sound insulating material whose characteristics are determined by surface density, rigidity in bending and internal loss. In a given frequency region, a larger weight results in a higher sound-insulating effect. For this purpose, high density resin mixtures in which large amounts of metallic powder, calcium carbonate or glass fibers are incorporated, or asphalt sheets have conventionally been in use.
The sound absorption is an absorption of vibration energy of sound as a heat energy by utilizing a viscosity resistance or frictional resistance of material so that reflection of sound waves is made small. To this end, materials having high voids such as open cell foamed plastics are used as a sound-absorbing material. Examples of such a sound-absorbing material include masses or boards of glass wool, asbestos, foamed urethane and the like, which are employed as shaped in conformity with various forms of surface material.
The vibration damping is to absorb an energy of vibrations or sounds transmitted through material as a heat energy converted as a result of deformation in shear or compression of the material. The vibration-damping material should favorably have a high loss coefficient and a high modulus of elasticity. The vibration-damping material is usually used after attachment to or coating on vibrating plates. Two types of the damping are known including a restriction type where a panel is attached on the vibration-damping material and a non-restriction type where no panel is used. Typical of the restriction type are vibration-damping steel sheets or plates of various types. Other vibration-damping materials include resins in which large amounts of particles such as of ferrites, metals, ceramics and the like, flakes such as of talc, mica and the like, and various fibers such as wollastonite and glass fibers.
The vibration insulation is achieved, for example, by inserting an appropriate spring between a vibration source and an object to be vibrated. The vibration insulating material acts as the spring, typical of which is vibration-insulating rubber.
In recent years, requirements for soundproofing have become very severe. There is a demand for soundproofing materials which have a high soundproofing efficiency and are rust-free and non-metallic in nature.